CASE 10222 Published on 18.07.2012

Pontine and Extrapontine Demyelinolysis: Osmotic Demyelination Syndrome

Section

Neuroradiology

Case Type

Clinical Cases

Authors

Arvinder Singh1, .Rajiv Sharma2, Sohan Singh1, Aakanksha Sriwastwa Gupta1

1. Radiodiagnosis Dept. Government Medical College, Amritsar, India. 2. Medicine Department, Government Medical College, Amritsar, India. Email: avinderdr@rediffmail.com
Patient

14 years, male

Categories
Area of Interest Neuroradiology brain ; Imaging Technique CT, MR, MR-Diffusion/Perfusion
Clinical History
An 18-year-old male presented with sudden development of dysarthria, confusion, seizures and deranged consciousness after undergoing haemodialysis for chronic renal disease. There was no history of fever, cough, breathlessness, or headache. He was non-vegetarian, non-alcoholic, non-diabetic and non-smoker. His neurological examination revealed brisk reflexes with extensor plantars.
Imaging Findings
Abdominal ultrasound showed markedly increased cortical echogencity of both kidneys with reduced corticomedullary distinction. No calculus or hydronehrosis seen on either side.

CT of the brain showed well-defined hypodensity in the basis pontis region with hypodensities in middle and superior cerebellar peduncles, reduced attenuation of midbrain. Hypodensities were seen in posterior limbs of both internal capsules (Fig. 1,2).

MRI of the brain showed diffuse hyperintense signal in pons, middle and superior cerebellar peduncles, in the brain stem, posterior limbs of internal capsules, basal ganglia and subcortical white matter both insular regions in T2-weighted and fluid-attenuated inversion recovery (FLAIR) images. T1-weighted images showed iso- to hypointense signal in pons and midbrain with minimal enlargement (Fig. 3,4). The MRI findings suggested osmotic myelinolysis (pontine and extrapontine), which developed as a complication of rapid correction of hyponatraemia associated with renal disease.
Discussion
Central pontine myelinolysis (CPM) is a non-inflammatory demyelinating disease of the pons characterized by loss of myelin, and was described by Adams in 1959. The concept was extended from 1962 with the recognition that lesions can occur at extrapontine sites, so-called extrapontine myelinolysis (EPM). The association of CPM with EPM was described as Osmotic Demyelination Syndrome (ODS). In 1976, Tomlinson credited with the suggestion that the rapidity of correction of Na+ was the aetiological factor [1].

The classic symptoms of osmotic demyelination syndrome are spastic quadriparesis and pseudobulbar palsy, which occur as a result of corticospinal and corticobulbar tract involvement in the pons and internal capsule [2].
In patients with end-stage renal disease, osmotic demyelination syndrome may develop as a result of osmotic changes during hemodialysis [3, 4].

CPM is predominantly a lesion of the basis pontis with relative sparing of tegmentum. The lesions of EPM occurs in midbrain, cerebellum, putamen, thalamus and caudate nucleus and cerebral cortex/subcortex [5, 6]. It is hypothesized that high osmotic changes associated with sodium imbalance causes endothelial injury in grey matter, which induces release of myelinolytic factors that damages adjacent white matter, hence the term osmotic demyelination [3]. The mechanism of myelinolysis is thought to be linked to intramyelenitic splitting, vacuolization and rupture of myelin sheaths [7, 8].
CT and MRI are imaging modalities used in diagnosis of ODS. Conventional CT is less sensitive than MR imaging . MRI is the imaging modality of choice in evaluating ODS.

CT may be normal in early stage but may show central hypodensity in pons with or without extrapontine manifestations [8].

T2-weighted MRI and fluid attenuation inversion recovery (FLAIR) sequences in CPM shows classical triangular or “trident-shaped” hyperintense area in central pons with sparing of the ventrolateral pons and corticospinal tracts, with corresponding iso- to hypointense signal on T1-weighted images.

The features of EPM on T2-weighted and FLAIR shows bilateral symmetrical areas of hyperintense signal in midbrain, lateral thalami, internal capsules, basal ganglia and cortico-medullary junction in peripheral cortex [9, 10].

Current literature demonstrates DWI to be sensitive at very early time points after ischemic injury [11, 12].
The management of ODS is prolonged neuro-rehabilitation, TRH administration, corticosteroids, plasmapheresis and intravenous immunoglobins [13, 14].
Differential Diagnosis List
Osmotic Demyelination Syndrome
Hypoxic encephalopathy
Multiple sclerosis
Brainstem Infarcts
Final Diagnosis
Osmotic Demyelination Syndrome
Case information
URL: https://eurorad.org/case/10222
DOI: 10.1594/EURORAD/CASE.10222
ISSN: 1563-4086